It is well known that coal piles having at least one surface exposed to the atmosphere suffer from a number of disadvantageous conditions. For purposes of this specification and claims, the term "pile" encompasses any conglomeration of coal lumps, e.g., stockpiled on the ground for use in industrial plants, electric utilities, and the like; stowed in open bins, railway freight cars, trucks, and the like; moved by conveyor; and the like.
Some problems which occur regularly in the storage and transportation of coal include the following:
1. Excess moisture in the body of coal caused by excessive humidity, rain, or snow results in: PA1 2. The free flow of air through the pile induces auto-oxidation of the coal which can reduce fuel value by as much as 5% or more in a year. Continued auto-oxidation can reach the point of spontaneous combustion, particularly in low-rank coals. PA1 3. Dust and acid leachates emanating from coal piles and conveyers create air and soil pollution and loss of fuel value. PA1 4. Wind and the motion of train or truck can result in:
(a) loss of fuel value (by as much as 3% or more) due to loss of heat to water evaporation during use; PA2 (b) Prevention of normal operation of grinding and pulverizing machinery which frequently cause outages in factory or electric utility operation; PA2 Water freezing which makes it very difficult to remove the coal from the storage pile. PA2 (a) physical losses of coal from the upper surface of the pile, and PA2 (b) generation of coal fines which are not physically usuable as fuel in many facilities and must be segregated and disposed of separately.
Efforts have been made to reduce these problems, but with limited success aside from the fact that they are excessively costly and none has been able to eliminate most of the problems. Layering and compaction of coal stores have been used to reduce void volume and minimize air circulation with only partial success. Costly oil sprays, which have been tried to reduce dusting and oxidation, have been only partially successful. Experiments have shown that spontaneous combustion can be eliminated by vapor deposition of Si0.sub.2 on the surface of the coal, but such a solution is impractically costly.
Although certain of the coating compositions containing pitch, alphalt, tars, and the like are somewhat similar to compositions known to the art for such use as roofing materials, mastic tile, the making of carbon articles, e.g., electrodes, and sealing compositions, none has been disclosed for the purpose of the present invention.
The coating of the present invention, when applied to the exposed surface of coal pile (as defined supra), melds into a hard, continuous coating which adheres well to the coal and, when applied to the entire exposed surface, forms an air- and moisture-impervious layer which protects the pile from the problems engendered by excessive moisture and air penetration. Additionally, it substantially eliminates dust and acid leachate emanations and protects piles in transit from physical due to wind and the motion of the vehicle and, because of the immobilizing effect of the hard, continuous surface layer, minimizes generation of coal fines due to frictional motion within the pile during transit.
Thus the surface layers of the invention substantially eliminate loss of fuel value, processing difficulties, and air and soil pollution by substantially eliminating auto-oxidation, spontaneous combustion, excessive moisture, dust emanation, obstructions to handling, wind and motion loss. The coating compositions are low cost, particularly where the lower cost binders and waste material fillers are employed. Their cost, furthermore, is substantially offset by their added fuel-value, since they contribute to the combustion process.